1. Field of the Invention
The present invention relates to a nonwoven fabric made from filaments and to artificial leather containing it. More specifically, the invention relates to a nonwoven fabric made from filaments which can be used with advantage as a base fabric for artificial leather, and to artificial leather made using the nonwoven fabric.
2. Description of the Related Art
Artificial leather used as a leather substitute in recent years has become popular among consumers due to its features such as lightness and ease of care, and it has come into wide use in the fields of clothing, general materials, sports, etc. However, artificial leather is desired to have a softness, a drape property which arises from the dense structure, and the like, as provided by natural leather, and several proposals have been set forth to provide such desired properties.
In particular, various nonwoven fabrics made from filaments have been proposed (Japanese Examined Patent Publication No. 44-29543, No. 60-12465, etc.) because, unlike nonwoven fabrics made from staple fibers, they do not require a series of large-scale equipment such as a staple fiber feed unit, opening machine, carding machine, crosslapper, etc. for their production, while being made from filaments, they have a major advantage of strength over tangled nonwoven fabrics of staple fibers.
In addition, since nonwoven fabrics made from filaments also require no carding step, unlike nonwoven fabrics made from staple fibers, there is no need to form high crimps into the fibers and filament nonwoven fabrics can be made directly from fine denier filaments, while the ratio of space between the fibers can be easily reduced to make the nonwoven fabric dense.
For an improved appearance, there has been proposed, in Japanese Examined Patent Publication No. 59-42108, a nonwoven fabric with excellent softness and excellent abrasion resistance, which comprises an intertwined nonwoven fabric made from a resin and an aggregate of fine denier filaments with a denier of 0.3 de or less and which exhibits a high tearing strength. However, at least one of the surfaces is a side formed by the filaments and the resin, and is different from a suede-like erected pili surface, or a smooth surface consisting of the polymer alone, i.e. a xe2x80x9cfull-grain surfacexe2x80x9d.
In Japanese Unexamined Patent Publication No. 3-213555 there is proposed a nonwoven fabric consisting of bicomponent splittable fibers. The patent publication states that the nonwoven fabric can be used for medical uses, for bags, and the like, but despite the high strength due to partial bonding of the fibers by at least the resin among the fiber forming components, there is too much repulsion, rendering it unsuitable particularly as artificial leather for clothing.
There is also proposed, in Japanese Unexamined Patent Publication No. 10-53948, a method whereby aggregates of splittable fibers as the starting fibers are subjected to force tangling by needle punching or a method of tangling by high pressure water stream, and a nonwoven fabric obtained by splitting the filaments is heated in boiling water or steam for heat shrinkage to achieve further densification.
Artificial leather obtained using a nonwoven fabric prepared in this manner has a high apparent density due to the heat shrinkage which also provides a densified structure, so that the artificial leather has a full and tight handling property, but it lacks softness, and, in the case of forming artificial leather with full grain wherein a coating such as a film consisting of high elastic polymer or the like is formed on the surface of the artificial leather, large buckling creases occur when the artificial leather is folded, constituting an inherent critical defect; thus, a problem occurring when such artificial leather, particularly full-grain artificial leather is used to produce shoes, bags, gloves or furniture, is that the initial appearance deteriorates with use.
On the other hand, even in the case of suede-like artificial leather, it has not yet been possible to obtain products with dense erected pili and a pleasant surface touch similar to natural leather, and therefore an artificial leather has been desired which is endowed with an natural leather-like feeling of softness and limited stretching, as well as a beautiful appearance.
It is a first object of the present invention to overcome the aforementioned problems of the prior art by providing a nonwoven fabric made from filaments with which it is possible to prepare artificial leather as full-grain artificial leather which exhibits both the softness and full and tight handling property of natural leather while also having no buckling creases upon folding and being resistant to formation of buckling creases, or nubuck-like artificial leather with an excellent fine touch similar to baby-skin, which has not existed in the prior art.
It is a second object of the invention to provide artificial leather which is prepared from the above-mentioned nonwoven fabric made from filaments.
The present inventors focused on the structure of nonwoven fabric as the reason for both softness and a tight handling property and excellent suede-like surface touch and as the cause of buckling creases upon folding of full-grain leather (hereunder referred to simply as xe2x80x9cbuckling creasesxe2x80x9d) in artificial leather prepared using nonwoven fabric made from filaments as the base fabric, and upon carrying out diligent research on the properties of nonwoven fabric structures made from tangled fine denier filaments and on methods for forming them, they have found that artificial leather with both softness and a tight handling property requires that the nonwoven fabric have a high density and that the number of fiber bundles oriented in the direction of thickness of the artificial leather be within a specific range.
It was also found that buckling creases in full-grain artificial leather which occur when using splittable-type multicomponent filaments are a result of the structure unique to splittable-type multicomponent filaments, wherein the splittable fine denier filaments are still in an aggregated state with the distance between them being close that that in the state of orientation as multicomponent filaments, with the nonwoven fabric including macrospaces of 800 xcexcm2 or greater. In other words, it was found that the buckling creases in full-grain artificial leather occur because of the multifilament state formed by aggregations of fine denier filament groups produced by splitting from monofilaments of the splittable-type multicomponent filaments, resulting in tangling of the splittable-type multicomponent filaments which forms macrospaces within the nonwoven fabric that are not filled by the fine denier filament groups.
On the other hand, it was also found that in the case of nonwoven fabrics made from filaments formed from islands-in-a-sea type multicomponent filaments, the feeling of softness and a full and tight handling property like natural leather, and the surface touch of nubuck-like artificial leather can be obtained by a specific structure having the fiber bundles described above, and by the properties arising from those fiber bundles, upon which the present invention was thus completed.
In other words, the first object of the invention can be achieved by a nonwoven fabric made of filaments, which comprises filaments formed from a fiber-forming thermoplastic polymer and satisfies all of the following conditions (A) to (D).
(A) The fiber bundles are present in a range of 5-70 per centimeter in any cross-section parallel to the direction of thickness of the nonwoven fabric.
(B) The total area occupied by the fiber bundles is in a range of 5-70% of the cross-sectional area of any cross-section perpendicular to the direction of thickness of the nonwoven fabric.
(C) The apparent density is 0.10-0.50 g/cm3.
(D) The cut ends of the fibers on the nonwoven fabric surface are present in a range of 5-100 per mm2 of surface area.
The second object of the invention can be achieved by artificial leather comprising the nonwoven fabric according to the invention and a polymeric elastomer impregnated therein and satisfies all of the following conditions (I) to (N).
(I) The fiber bundles are present in a range of 5-70 per centimeter in any cross-section parallel to the direction of thickness of the artificial leather.
(J) The total area occupied by the fiber bundles is in a range of 5-70% of the cross-sectional area of any cross-section perpendicular to the direction of thickness of the artificial leather.
(K) At least a portion of the impregnated polymeric elastomer is polymeric elastomer which is not fixed among the fibers.
(L) The tensile stress at 20% elongation ("sgr"20) in the warp direction and the tensile stress at 20% elongation ("sgr"20) in the weft direction of the artificial leather are each in the range of 1.5-10 kg/cm.
(M) The ratio of the 20% elongation ("sgr"20) in the warp direction to the bending resistance (Rb (g/cm)) for the artificial leather and the ratio of the 20% elongation ("sgr"20) in the weft direction to the bending resistance (Rb (g/cm)) for the artificial leather have an average value of 3-30.
(N) The apparent density of the artificial leather is 0.20-0.60 g/cm3.